A diffuse, veil-like layer of
ice crystals at high
altitude, sometimes miles thick. Very often gives rise to a
22º halo, and every once in a while a
46º halo; this is one way to tell a cirrostratus from an
altostratus, which is veil-like cloud mainly composed of liquid water. A cirrostratus is often associated with the coming of
low pressure, so
wind and
rain frequently occur within a day or so of its being seen.
Occasionally written cirro-stratus.